GCN Circular 31746

Aaron Tohuvavohu (U Toronto), James DeLaunay (UAlabama), Gayathri
Raman (PSU), Jamie A. Kennea (PSU), report:

Swift/BAT did not localize GRB 220310C onboard (T0:
2022-03-10T22:23:51 UTC, Fermi/GBM GCN 31735
Not found
 
 
).

The Fermi notice, distributed in near real-time, triggered the Swift
Mission Operations Center operated Gamma-ray Urgent Archiver for Novel
Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).

Upon trigger by this notice, GUANO sent a command to the Swift Burst
Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from
[-50,+150] seconds around the time of the burst. All the requested
event mode data was delivered to the ground.

The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu,
arXiv:2111.01769
Not found
 
 
), detects the burst in a 8.192 s analysis time bin
with a sqrt(TS) of 9.7.
A candidate arcminute localization is found with DeltaLLHOut of 19.7
and a DeltaLLHPeak of 5.7.

For this reason we can confidently claim detection, and preference for
an in FOV origin, but the best fit arcmin localization is not strongly
preferred over other positions.
A few burst locations with comparable DeltaLLHPeak have been
previously verified with afterglow discovery (eg GRB 211106A).

See Section 9.1 and Figure 20 in the NITRATES paper for brief
descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and
DeltaLLHOut.

No source is found with conventional BAT imaging. This is expected
given the strength of the signal in BAT, and its position near the
edge of the coded FOV.

The BAT position is
RA, Dec = 290.069, +40.253 deg which is
   RA(J2000)  = 19h 20m 16.62s
   Dec(J2000) = +40d 15��� 12.3���
with an estimated uncertainty of 5 arcmin.

This independent position is consistent with the Fermi/GBM
localization (GCN 31735
Not found
 
 
).

XRT and UVOT follow-up has been requested.
Results of follow-up observations will be reported in future circulars.

GUANO is a fully autonomous, extremely low latency, spacecraft
commanding pipeline designed for targeted recovery of BAT event mode
data around the times of compelling astrophysical events to enable
more sensitive GRB searches.

A live reporting of Swift/BAT event data recovered by GUANO can be
found at: https://www.swift.psu.edu/guano/